The present invention concerns a method and a device for sorting products.
It is meant in particular for removing certain products from a product stream.
In particular, it aims a method and a device which is very suitable to be applied in the food industry, for example for sorting out non-food products from certain foods, in particular leaves, branches and pieces of waste such as wood, plastic, stones, etc.
However, the products to be sorted can also be foods of different quality, whereby a quality selection is made by means of the sorting. The method can also be used to separate good and bad products.
It is known from the international patent application WO 96/00621 to illuminate the products to be sorted with a light beam and to subsequently carry out a selection on the basis of the light which is collected by means of reflection, fluorescence or such. The collected light is treated in a spectroscopic analysis device which delivers an output signal for the selection as a function of the analysis. As use is made of a spectral analysis, whereby the entire spectrum has to be analysed every time, this system is very expensive since it requires a spectroscopic analysis device.
A method is known from the international patent application WO 97/42489 to determine the ripeness of seeds by means of the fluorescence of the chlorophyll in the seeds, after they have been illuminated. The described method makes it possible to shine light through the seeds one after the other, but it does not offer a practical embodiment for the treatment of large amounts at once. Moreover, the described method only leads to a selection among seeds, but it does not go in the direction of selecting strange products from foodstuff or such.
A method for sorting particles is known from the patent application GB 2.292.455, whereby the particles to be sorted are irradiated with a laser and the obtained xe2x80x98Raman scatteringxe2x80x99 is used as a sorting criterion. As exposed in GB 2.292.455, normal Raman scattering is disadvantageous in that the signal obtained by means of xe2x80x98scatteringxe2x80x99 is disturbed too much by the xe2x80x98emissionxe2x80x99 obtained by means of fluorescence, and thus becomes difficult to detect. That is why it is suggested in GB 2.292.455 to make use of a stimulated Raman signal. However, this technique is in turn disadvantageous in that a high energy supply is necessary, requiring expensive equipment.
In general, the invention aims a method and a device which make it possible to carry out a very efficient and reliable selection in a large product stream, such that the sorting can be applied at an industrial level for the treatment of large quantities of products.
In particular, according to a number of preferred embodiments, it aims a method and a device whereby the use of expensive spectrographical analysis equipment is excluded, and whereby large quantities can be treated.
To this aim, the invention in the first place concerns a method for sorting products, characterised in that it at least consists in conveying the products to be sorted in the shape of a product stream, extending in the width, over a specific path; in scanning the products to be sorted over the width of said product stream, by casting light onto the products on the one hand, at least in a specific spectrum which is selected such that certain products of the products to be selected will emit light, and by observing this light in a specific range of the spectrum in which the emitted light is cast on the other hand; in making a selection between the scanned products as a function of the observed light; and in automatically separating the products from the above-mentioned product stream as a function of said selection.
By making use of a wide product stream which is scanned over the width on the one hand, and by making use of emitted light on the other hand, it is possible to make a particularly fast and efficient selection with great certainty and with a minimum of faults, such as opposed to for example the above-mentioned known systems, as well as the systems which are available on the market, whereby the selection is exclusively made on the basis of reflected light, in particular by means of colour recognition.
By making use of a spontaneous xe2x80x98emissionxe2x80x99, by which is mainly implied xe2x80x98fluorescencexe2x80x99 as will be further explained, the effect which is felt as being disadvantageous according to GB 2.292.455, will be used as an essential characteristic according to the invention to carry out the selection. This effect is particularly useful when sorting specific foods, whereby Raman scattering does not offer an efficient solution.
Preferably, in order to observe the light which is emitted by the products concerned, use is made of an optical filtering, in particular by means of an optically adjusted filter, for example a band-pass filter. This allows for an almost instant evaluation and selection of the scanned products, as opposed to the relatively complicated and expensive spectral analysis which is applied in the method described in WO 96/00621.
The selection is preferably made on the basis of a certain intensity value of the emitted light or of a signal corresponding to it being either exceeded or just not exceeded. As use is made of the emission in a specific spectrum, there is a very clear distinction between signals which are related to a light-emitting product and signal which are related to a non-light-emitting product, which makes it possible to make a very efficient distinction by simply verifying whether the signals either or not exceed a certain value.
In particular, the light is preferably cast from such a part of the spectrum that light is emitted by the products concerned in another part of the spectrum. This makes it easy to make a distinction between the emitted light and possibly directly reflected light by means of an optical band-pass filter or such.
According to the most practical embodiment according to the invention, use is made of the fluorescence qualities for the emission, in particular the fact that the scanned products either or not fluoresce.
More in particular, the method will be used for sorting chlorophyll-containing foods, in particular for the selection of strange products from foods.
The invention is particularly useful for separating waste from for example peas, especially for separating strange products therefrom such as stones, pieces of wood, plastic and such.
In the case where the method is applied for separating waste from products containing chlorophyll, such as for example peas, light is preferably emitted during the scanning having a wavelength in the order of magnitude of 640 to 680 nanometer, whereas other light is preferably excluded. Thus, only the foods containing chlorophyll, in this case the peas, start to emit light in the spectrum to be observed as a result of fluorescence. This wavelength selection can also be used for other foods containing chlorophyll, such as beans, lettuce, sprouts, etc.
In order to observe the emitted light, observations are preferably exclusively made in the wavelength range of 690 to 740 nanometer, preferably by means of optical filtering, and in particular in a range which has a value in the order of magnitude of some 715 nanometer. In this range, the emission can be optimally observed.
According to another application of the invention, use is made for the emission of the light-emitting quality of certain organisms such as bacteria, fungi and such, which can be found on certain products, whereby a selection is made between the products on the basis of said emission.
A practical application thereof according to the invention consists in sorting foods which are affected by fungi from non-affected foods, in particular in sorting nuts or figs which are affected by aflatoxins. Preferably, there will be an excitation with deep blue UV light (340 to 400 nm). The observed emitted light will then be green. Preferably, measurements will only be carried out in the wavelength range of 440 to 550 nm in this case.
According to a major variant of the invention, use is made of a background which will emit light when it is being illuminated, in particular which will fluoresce, such that the light being cast will also produce an emission effect in those places where it is not cast on a product. This offers the advantage that it becomes possible to make a simple selection between light-emitting and non-light-emitting products without any special measures being required to prevent that those places where there is no product and which are observed during the scanning are regarded as places where strange products to be removed are found.
Use is preferably made here of an emitting background of a surface extending in the width of the product stream which is spherical on the side where the light is cast upon. The spherical shape promotes a very precise emission.
Practically, the above-mentioned background will consist of a cylindrical roller.
According to a special embodiment, instead of using a background which emits light after light has thus been cast upon it, use can also be made of a background which constantly emits light, preferably of a wavelength which is ideal in relation to the selection to be made.
As for the emitting background, a background is preferably provided which emits light having a wavelength of the same order of magnitude as the light which is emitted by the products to be treated.
In order to be able to obtain high emission values with a minimum of energy, and consequently to be able to make observations with great certainty, the scanning according to the invention is preferably carried out by means of a laser, in particular by making a laser beam move diagonally over the product stream in a systematic manner.
According to a very advantageous embodiment, a scanning system with a moving mirror, preferably a rotating polygon mirror or another optical element is used, and the emitted light is returned via the same mirror or the same optical element.
Instead of making use of a laser, the scanning can also take place in another way, for example by means of a fixed light band or a series of light points, directed onto the products which pass by over the width of the product stream, whereby at least the emitted light is observed by means of a camera, and whereby the selection is made on the basis of the evaluation of camera images.
In order to make the products move in the shape of a product stream with a certain width along the place where they are scanned, use can be made of different techniques. A practical technique consists in bringing the products in a single plane on the place where they are to be scanned, via a table, belt or such, either or not provided with longitudinal ducts or grooves.
Further, the products preferably fall down freely and the products to be separated are moved apart by means of nozzles which are erected over the width of the product stream and which are individually activated as a function of the observations made, whereby for example the products to be removed from the global product stream are blown away and are collected in a recipient.
In order to further optimise the method, the products to be sorted can be scanned from two sides, situated opposite to the product stream. This makes it possible to make a right selection with more certainty, which is particularly important when there is a possibility that products show different qualities on the front and on the back side.
It should be noted that the method of the invention can possibly be combined with another scanning process, for example with a colour sorting by means of the reflected light. In the latter case, different laser beams can be used, namely at least one laser beam to realise the above-mentioned emission in a different spectrum, and at least one laser beam for sorting for example on the basis of the normal light reflection. Practically, the different laser beams can then be simultaneously guided along the same light path according to the invention, possibly slightly shifted in relation to one another. As a result, only one polygon mirror or another optical element will be required to move the laser beams over the product stream.
Apart from the above-mentioned method, the invention also concerns a device for sorting products according to the method, characterised in that it at least consists of the combination of means for conveying the products to be sorted-in the shape of a product stream extending in the width over a certain path; means for scanning the products to be sorted over the width of said product stream, consisting of means to cast light on the products on the one hand, at least in a specific spectrum which is selected such that specific products to be sorted will emit light, and of means to observe this light in a specific range of the spectrum in which the cast light is emitted, on the other hand; means to make a selection between the scanned products as a function of the observed light; and means to automatically separate the products from the above-mentioned product stream as a function of said selection.